From 112a62ddb32952943517bd170f0eeb26a6f0738f Mon Sep 17 00:00:00 2001 From: john stultz Date: Thu, 8 Oct 2009 13:31:45 -0700 Subject: [PATCH] PIT fixes to unbreak suspend/resume (bug #14222) Resolved differently upstream in commit 8cab02dc3c58a12235c6d463ce684dded9696848 Ondrej Zary reported a suspend/resume hang with 2.6.31 in bug #14222. http://bugzilla.kernel.org/show_bug.cgi?id=14222 The hang was bisected to c7121843685de2bf7f3afd3ae1d6a146010bf1fc however, that was really just the last straw that caused the issue. The problem was that on suspend, the PIT is removed as a clocksource, and was using the mult value essentially as a is_enabled() flag. The mult adjustments done in the commit above caused that usage to break, causing bad list manipulation and the oops. Further, on resume, the PIT clocksource is never restored, causing the system to run in a degraded mode with jiffies as the clocksource. This issue has since been resolved in 2.6.32-rc by commit 8cab02dc3c58a12235c6d463ce684dded9696848 which removes the clocksource disabling on suspend. Testing shows no issues there. So the following patch rectifies the situation for 2.6.31 users of the PIT clocksource that use suspend and resume (which is probably not that many). Many thanks to Ondrej for helping narrow down what was happening, what caused it, and verifying the fix. --------------- Avoid using the unprotected clocksource.mult value as an "is_registered" flag, instead us an explicit flag variable. This avoids possible list corruption if the clocksource is double-unregistered. Also re-register the PIT clocksource on resume so folks don't have to use jiffies after suspend. Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/i8253.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c index 5cf36c053ac4..da890f03d078 100644 --- a/arch/x86/kernel/i8253.c +++ b/arch/x86/kernel/i8253.c @@ -21,8 +21,10 @@ EXPORT_SYMBOL(i8253_lock); #ifdef CONFIG_X86_32 static void pit_disable_clocksource(void); +static void pit_enable_clocksource(void); #else static inline void pit_disable_clocksource(void) { } +static inline void pit_enable_clocksource(void) { } #endif /* @@ -67,7 +69,7 @@ static void init_pit_timer(enum clock_event_mode mode, break; case CLOCK_EVT_MODE_RESUME: - /* Nothing to do here */ + pit_enable_clocksource(); break; } spin_unlock(&i8253_lock); @@ -200,19 +202,27 @@ static struct clocksource pit_cs = { .shift = 20, }; +int pit_cs_registered; static void pit_disable_clocksource(void) { - /* - * Use mult to check whether it is registered or not - */ - if (pit_cs.mult) { + if (pit_cs_registered) { clocksource_unregister(&pit_cs); - pit_cs.mult = 0; + pit_cs_registered = 0; + } +} + +static void pit_enable_clocksource(void) +{ + if (!pit_cs_registered && !clocksource_register(&pit_cs)) { + pit_cs_registered = 1; } } + + static int __init init_pit_clocksource(void) { + int ret; /* * Several reasons not to register PIT as a clocksource: * @@ -226,7 +236,10 @@ static int __init init_pit_clocksource(void) pit_cs.mult = clocksource_hz2mult(CLOCK_TICK_RATE, pit_cs.shift); - return clocksource_register(&pit_cs); + ret = clocksource_register(&pit_cs); + if (!ret) + pit_cs_registered = 1; + return ret; } arch_initcall(init_pit_clocksource); -- 2.39.5